Whole eggs and their yolks, particularly chicken eggs, contain nutritionally physiologically valuable components such as proteins, for instance vitellin, phosphorous lipids (lecithins), as well as medically undesirable materials such as cholesterol. Cholesterol is present in the fat fraction of the egg yolk and, together with the equally undesirable saturated fatty acids, amounts to about 20% of the valuable weight of the yolk.
For numerous health and dietary reasons, it is especially desirable to reduce the cholesterol proportion in the yolk. In this regard, many attempts have been made to remove the cholesterol from eggs and egg yolks.
Attempts to achieve cholesterol reduction have included removal of the fat fraction of the egg yolk by total extraction with a solvent such as hexane. While this procedure allows removal of the cholesterol, it also has the undesirable side effect of removing or extracting, all or in part, the medically desirable lecithins. Moreover it is impossible to entirely remove the extractant, for instance hexane, from the egg yolk without thereby harming the product. Another way to remove cholesterol from the egg yolk is by means of high-pressure extraction using super-critical fluids such as CO.sub.2. High-pressure extraction allows selective removal of the cholesterol together with other fats contained in the egg yolk without thereby reducing the lecithin content. However this procedure incurs the drawback of very long treatment times since the cholesterol is absorbed by the fluid flow as the last substance of the egg-yolk fat fraction. As a result, partial denaturing of the egg yolk proteins easily take place at the temperatures and pressures required for high-pressure extraction.
Another way to remove cholesterol from yolk is by adding cyclodextrin to the liquid yolk. Cyclodextrin selectively encloses cholesterol. Following a given time of application, the cyclodextrin together with the enclosed matter can be removed from the yolk. But on economic grounds this procedure is not yet widely marketed.
Other treatment processes, such as that shown in Japanese Patent No. 63-109757, have attempted to reduce the cholesterol content of the egg or egg yolk by vigorously mixing it with an extractant in which the cholesterol is soluble. To maximize the surface area of the egg exposed to the extractant fluid, and thus maximize the extraction of the cholesterol, very small particle sizes are vigorously agitated with the extractant in a homogenizer. However, this has resulted in changes to the egg product that adversely affects the flavor and the texture. The high shearing action alters the protein structures in the egg as well as the structures of other components.
Accordingly it is the object of the present invention to create a medically acceptable method for the preparation of cholesterol-reduced, full egg or egg-yolk products which has a taste similar to that of fresh eggs or egg yolks. Another object of the invention is to make available especially appropriate cholesterol-reduced, full egg or egg-yolk products.